The quality of our road network in the UK is famously bad. Manufacturers do us no favours by selling countless models with overly firm suspension and tyres with wafer-thin sidewalls, but ultimately it’s the interconnected spaghetti of pockmarked black stuff that’s at fault.

That got us thinking: what if it didn’t exist? Well, over the next two days we’re going to find out. More precisely, we’re going to attempt to drive from coast to coast – east to west Scotland, from Novar to Ullapool – without once using a road. A feat we understand no-one has ever attempted.

Along the way we’re expecting to scale rocks, wade through streams and rivers, and tackle miles of mud and gravel. Clearly we’re going to need a car that’ll be up to this rather daunting task, but what to pick? It needs to be something with genuine terrain-tackling ability, a decent reliability record and preferably heated seats. It is November in Scotland, after all.

Come on then! Tell us what you picked…

Let us introduce you to our choice, then: it’s the seven-seat Mercedes-Benz GLS 350d 4Matic Designo Line. You can read our thoughts on this car here, but this particular one’s got a few special bits of kit.

First and foremost, we’re going to need some decent rubber, so Atturo Trail Blade off-road tyres are the order of the day. Second, we’ve got a set of wellies just in case we get stuck and there’s a support vehicle with satellite Wi-Fi so we can keep you updated. That’s it. Just a fool, a 4x4 and a phone.

WNL would set you back £78k with no options, or a mighty £82,920 with all its options fitted. The main one that matters is the £1985 Off-Road Package, netting a 100% locking centre diff, more underbody protection, an Off-Road+ driving mode, three additional ride heights and a low-range gearbox function.

That little lot should set us up nicely for the challenge, we think you’ll agree, but what car would you have chosen? Have your say now via Twitter as we begin our journey, and follow the event using the hashtag #coasttocoast.

Read on to find out how we get on – we’ll be posting tweets, updates and pictures as we go along.

16:58, day 2 – The 18th hole

As we neared the end of our route the scenery changed and so did the roads. We descended towards Ullapool and the small seaside town’s golf club, leaving the lochs behind. We’d been allowed to drive on the course itself to get to the sea, and doing so completed a momentous off-roading challenge. We don’t think anyone’s ever done this before, and thanks to the generous cooperation of several local land-owners it was possible just for one day. Even as this is written the routes are being shut off again and peace is restored to this beautiful area of the world.

The GLS was the ideal companion for this adventure. It was arguably too comfortable, highly capable and easy to live with. It’s not a perfect car by any stretch, but you can rest assured that when it matters, it’ll be up to almost any challenge the UK’s countryside.

14:42, day 2 – Sharp shrapnel

The section after the bog was littered with billions of shattered rocks. We were skirting a number of lochs and the surrounding terrain featured loose stones, mud and the occasional stream. The main danger here was puncture to the chunky Atturo tyres, but there was also a secondary hazard in the form of potentially slipping off a ledge and falling to our deaths.

Thankfully neither happened, though we did have some hairy moments dipping the nose into ravines – we were convinced the overhangs were just too long for the angles required, but not once did it catch at front or rear.

At one point we waded through a muddy stream that came a long way up past the lower door shuts, though, but the quilted leather stayed bone dry.

13:35, day 2 – Trip to the bog

After lunch it was time to tackle the notorious boggy section. We had been warned that this was the area our car – and all the others – would struggle with the most. The problem was the saturated mud, which was more than happy to swallow a welly if you stood on the wrong bit.

In fact, it would become clear that at some points this area was waist-deep liquid – despite looking deceptively like terra firma.

For this reason we needed to employ some snow ladders (proper off-roading gear) and a couple of creative lines to conquer the worst of it.

You’ll have to wait to see the pictures taken of our endeavour, but suffice to say it’s unlikely you’ll ever see a GLS-class in such a compromised pose ever again.

But we did it, and soldiered on through the wilderness once more.

11:10, day 2 – Forging ahead

It’s harder work today. Snow is forecast for the afternoon and we’ve had repeated severe weather warnings along the way.

The GLS seems quite at home in these highland surroundings, which seems at odds with its crossover nature. It’s less wieldy that the rest of the crew’s G-Classes and you can’t see the corners of the car anywhere near as well, which makes tackling the more difficult inclines and articulations a challenge.

However, during the trip, we’ve watched TV in the middle of a wind farm and had seat heating, ventilation and massage available for the duration. Impressive stuff, considering the terrain we’ve tackled.

The gearbox continues to make the going a little less controllable than we’d like, but a bit of jerkiness is a small price to pay for the versatility on offer here. This is a car that’ll cruise for hundreds of miles in comfort and then scale a steep hill with minimal fuss. We just have to keep reminding ourselves of that fact.

20:37 – Rounding off the first day

As we pulled into the Alledale it gave us a chance to reflect on the day’s activities. The car hadn’t missed a beat, meaning we’d chosen well, and it had passed through scenery you simply have to see to believe.

Tomorrow we take on part two, however, which includes a notorious bogland section that is expected to leave our seven-seater foundering. Can’t wait…

16:40 – Tackling the tricky bits

Forgive me for not taking enough pictures while doing so, but you’ll have to take my word that we’ve done some incredibly challenging off-roading today.

I have to say that I’m impressed a car of this size made it to our lunch stop. The seven-seat GLS – a car that’s far more likely to be spotted in Waitrose carpark than anywhere remotely remote – has been nudged down tiny mud tracks strewn with rocks and streams, and made its way up and down steep, slippy slopes.

We’re driving the only GLS here; most of the rest of our group in far more capable G-Wagons and one in a smaller GLE. That means we had the biggest overhangs, as well as just the one locking differential compared to the G’s three.

So, while we were able to watch TV in the middle of Scotland’s first wind farm with our massaging, ventilated and heated seats pampering our backsides, we weren’t guaranteed success by any means. In fact, at one point we came within centimetres of ripping the front bumper right off the car as we dove into a river, but thankfully we managed to stop just in time, reverse and try a different line.

One thing that did take a bit of getting used to was the off-road kit, and how it works with the car to safely get you down challenging terrain. It’s unlikely this is a problem with the car, and probably user error, but we found the automatic gearbox kept jumping into second gear when we weren’t expecting it while descending steep hills. This would cause a momentary jump forwards before the Downhill Speed Regulation system caught up and set our speed back to what we’d chosen using the cruise control stalk. As you can imagine, this is alarming when you’re not expecting it!

11:17 – stage one complete

The first part of our journey has taken us a few miles over the Novar estate and up a hill overlooking Cromarty Firth.

We had to engage all of the GLS's off-road gear to make decent progress, including its low-range mode, tallest ride height setting and off-road+ mode on the Dynamic Select rotary dial – which locks the centre diff and sets the off-road algorithms for the ESP, ABS and powertrain systems.